Chemical process



. Poiooiod Juno 1s, 1939 UNITED STATES 2,161,198 CHEMICAL Pnocsss Alberts. Carter, wummgton, nel., mignonto E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation oi' Delaware .Application ootobor 15,1937, congruo. 169,170

3 Claims.

This invention relates to the removal of vola.- tile constituents fromliquid` compositions comprising polymerizable derivatives of acetyleneby passing an inert gas through said liquid com- 5 position to entrainthe volatile constituents.

The polymerization of acetylene to nonbenzenoid polymers thereof may becarried out in successive steps. The rst formed polymers furtherpolymerize to produce polymers of greater molecm ular weight. As thispolymerization proceeds, the nature of the polymers change from gaseousmaterials to liquids of high fluidity, to oily liquids,

to gummy materials and finally to hard insoluble solids. 1t is oftendesirable to stop polymerization at an intermediate stage and therebyproduce intermediate polymers having valuable chemical and commercialproperties. When polymerization is thus interrupted, a mixture ofmaterials is obtained. Attempts to separate such mixtures f, bydistillation have been made. `Separation by distillation has beensuccessful but is invariably accompanied by a considerable loss ofproduct due to further polymerization. Moreover, difficulties areexperienced in carrying out continuous processes. More particularly,where one of the prode 255 ucts is an oily liquid and where it isdesired to remove from this oily liquid the more volatile lesspolymerizable materials by distillation, the oily polymers furtherpolymerize producing gummy and hard substances which clog the ap- 39paratus. This necessitates frequent shutdowns for the purpose ofdiilicult and costly cleaning of apparatus. The disadvantages hereindescribed are also met with in separating vinylacetylene from lessvolatile, heat polymerizable divinylacet- 35 yiene. volatneconstituents" as used 1n this specification and the claims meansconstituents having lower boiling points than the heat polymerizablematerial in the liquid composition, said constituents also having anappreciable vapor 49 pressure below the temperature at -Which heatpolymerization of the polymerizable material taires place in substantialamount.

It is an object of this invention to remove vola- A tile constituentsfrom compositions containing second stripping column 4 at 5, passesdown- 10 ward through saidcolumn and is drawn oi from 'the bottom at 6.Inert gas is introduced at the bottom of the second column 4 at l,passes upward entraining the volatile constituents and is vented fromthe top of the column at 8. The w mixture of gases ows through conduits9 and iii to condenser li where the volatile constituents are liquifiedand drawn off at l2. The inert gas' leaves condenserv ii at la andpasses through pump'ii, conduit it, rotometer it and into the 20 bottomof the rst stripping column i at il. The inert gas passes upward throughcolumn i entraining the-volatile constituents and is vented from the topat i t whence it passes through conduit i9, mingles with the vent gasfrom column in conduit iii and passes to condenser ii for separation andrecirculation. The flow of inert gas through column l is maintainedsubstantially constant with `the aid of rotometer i6. Part oi' the inertgas from condenser il, equal in amount to that introduced at i is toppedoff at 2e 3 and discharged. By operating in this manner, the liquidcomposition is contacted in the rst stripping column by recirculatedinert gas which removes most oi the volatile constituents. The liquidcomposition is then contacted in the second stripping column by inertgas of high purity and leaves said column substantially free of volatileconstituents. During this process, suitable temperature controlsmaintain the liquid composition at a temperature below that at which 40the heat polymerlzable material is polymerized in substantial amount. Itis to be understood that the drawing is a mere diagrammatical ow sheet.The drawing is not to scale and no attempt has been made to show detailswhich are unnecessary Ato an understanding of the process.

By way of specic example, one installation for ,the removal ofdivinylacetylene from a liquid 2 amigos outlets as shown in the nowsheet. 'Il'he second column is identical with the first one except insize. liIt is 12 feet high and 7. inch in diameter and the wire spiralis constructed of 10 gage (0.040 inch) stainless steel wire. Thecondenser, pump and -rotometer are all of conventional type and theapparatus is connected by suitable conduits as shown in the ilow sheet.Approximately 28 pounds per hour of a crude liquid composition isintroduced into the top of column I and 2. This liquid has a compositionof about 5% xylene,

l0 to 15% of oily acetone-soluble divinylacetylene polymers and 8 0 to85% of unpolymerized divinylacetylene. With the jacket temperature heldat 65 C. the temperatures in the column vary from 45 C. at the top to 55C. in the middle and about l25" C. 'at the bottom, this variation beingdue to the chilling effect oi.' the cold gas and the vaporizatlon of thevolatile constituents. Nitrogen 'is circulated around the cycleincluding. stripping column I, condenser il, pump I4 and rotometer I0 atthe rate` of '165 cu. ft. per hour. Pure nitrogen is introduced into thebottom of the second stripping column at a rate of about 55 cu. ft. perhour and the average temperage of this column is about 45 C. The liquiddischarged from the bottom of the second stripping column consistsofapproximately 3 to 4 lbs. per hour of polymers which contain less than0.5% of divinylacetylene, xylene and other volatile constituents. Theeiliuent gases from he first and second stripping columns are com -inedand enter condenser li where the entrained -vapors are condensed out ofthe circulating` nitrogen stream.l When the stripping apparatus. isoperated in connection with an apparatus for polymerizingdivinylacetylene, the condensate from condenser Il is returned with.fresh divinylacetylene to the polymerizer for further conversion to theoily relatively non-volatile polymers.

VNumerous variations are possible in the ar rangement and nature oftheapparatus used for carrying out the process of this invention. VAnyapparatus which produces eilcient contact between the inert gas and theliquid composition from which volatile constituents are to be removedmay be used. For example, instead`of the column described, columns maybe used which are packed with copper or glass rings, carborundum,

`chain or other materials suitable for packed co1- umns. Plain columnsmay also be used. Various gas distributors may advantageously be used inthe stripping column or chamber. One stripping column may be used or twoor more stripping columns may be employed in parallel, in

series or some in parallel .with some in series.

Pumps, valves, flow meter, temperature and pressure control apparatusmaybe placed wherever uents of the liquid composition being treated,

may be used in the stripping' .operation and the term inert gas is usedto signify such a nonliquid fluid. Those inert gases are preferred whichsatisfy these conditions at a lpreferred temperature (between 20 and 45C.) and atmospheric pressure. By way of example. the follown l ing gaseshave been found vto be satisfactory in the process of the specificexample: nitrogen, hydrogen, carbon dioxide and the inert gases of thezero group of the periodic table.

The process may be operated `at any convenient pressure. The use ofvacuum assists the process in some respects but .the disadvantagesgenerally outweigh the advantages. In general, it is most convenient tocarry out vthe stripping at vor slightly above atmosphericpressure.'I'he temperature of v the stripping operation may be controlled withing v suitable limits. .Since it is an object of this invention to preventfurther polymerization by heat, it is desirable to .keep the temperatureas low as possible, consistent with eilicient stripping. It has beenfound .that stripping can be eiliciently accomplished at between and 45C. at atmospheric pressure in the case of the specific example. peraturebe high enough to producepolymerization of the heat polymerizablematerial in sub-v divinylacetylene is heat polymerized in substan- -tialamount. A

2. A` process for removing divinylacetylene from a liquid compositionwhich comprises an oily acetone-soluble polymer of divinylacetylene,which process comprises passing said liquid composition through astripping zone and simultaneously passing an inert gas in4counter-current contact with said liquid in the stripping zone whilemaintaining the zone at a temperature between 20 and 45 C. which isbelow that at which said polymer is polymerized in substantial amount.

.3. A process for removing divinylacetylene from a liquid compositionwhich comprises. an

v oily acetone-soluble polymer of divinylacetylene.

which process comprises passing said liquid composition downward througha first stripping zone, circulating an inert gas upward through said rststripping zone, then through a condenser to remove volatile constituentsentrained in said stripping zone and then back through said strippingzone, passing said'li'quid composition from the bottom of the mststripping-zone to the top of a. second stripping zone and downwardthrough said second zone, passing inert gas of high purity into thebottom oi the second stripping zone, venting said gas and entrainedvolatile constituents from the top of said second stripping zone,

mingling said vent gases with the vent gases of the first stripping zoneat a point prior to'the passage of said gases through the said condenserand removing a portion of the inert gas from the system at a pointbetween that at which it leaves the condenser and that at which itenters the ilrst stripping zone, the temperature in the stripping zonesbeing maintained between 20 and 45 C.

vALBERT' s. CARTER.

In no event should the tem-

